1. Field of the Invention
The present invention relates to a ready for rotation state detection device, a method of detecting a ready for rotation state and a substrate processing apparatus.
2. Description of the Related Art
When a wafer is transferred into a processing chamber of a single wafer processing epitaxial growth apparatus, the wafer warps because a temperature surrounding the wafer rapidly changes from room temperature to 500 degrees C. or more. Such a warpage of the wafer subsides when the temperature of the wafer increases and reaches a temperature close to the surrounding's high-temperature environment. However, because the wafer behaves in a way that warps once and then decreases its warpage, when the wafer is placed on a susceptor with the warpage, a back side edge of the wafer may scratch the susceptor when the warpage decreases, which may generate dust.
Accordingly, as disclosed in Japanese Laid-Open Patent Application Publication No. 10-294287, an epitaxial growth apparatus is known that relays and supports a wafer by lift pins before transferring the wafer onto a susceptor while monitoring a warpage in the neighborhood of the center of the wafer by a CCD (Charge Coupled Device) camera, and transfers the wafer on the susceptor after the warpage of the wafer subsides by heating the wafer.
The invention disclosed in Japanese Laid-Open Patent Application Publication No. 10-294287 can prevent the wafer from performing a recovery action from the warped state on the susceptor, which can reduce contact between the backside edge of the wafer and the susceptor that is caused during the recovery action of the wafer from the warped state, and can prevent the backside edge of the wafer from being damaged.
However, in the configuration disclosed in Japanese Laid-Open Patent Application Publication No. 10-294287, because the recovery of the wafer from the warped state is determined depending on whether a shape of the wafer on the lift pins has become the same as a shape of the wafer when the wafer does not warp, transferring the wafer has to be started after the warpage of the wafer almost completely subsides, which takes a long time for transferring the wafer.
In the meantime, in a turntable-type substrate processing apparatus using a turntable, in general, there is a concave portion like a pocket (a depression) to fix a wafer provided in a surface of the turntable. Hence, when the wafer fits in the concave portion and the wafer is expected not to fly out when the turntable is rotated, a bit of remaining warpage does not harm the substrate process in most cases. Moreover, it is preferable for the substrate process to start as soon as possible after processing the substrate is ready to start to improve the throughput.